In terms of your domain, I would do what is best for your business long term. It sounds like you have a plan, don't let prior traffic dictate your business plan unless the expired domain fits in nicely. That previous traffic and links of a previous domain might not be helpful to your business. To me that should be icing on the cake if it's quality traffic and links, not garbage ones.

You do SEO work to build that traffic and it sounds like you have a pretty good head on your shoulders budget / expectation wise. Not a sprint but a marathon.

You can PM me if you would like some recommendations on companies that might be able to help you out. I would do a lot of homework though, the fact that you're offering up a strong four digit budget will put a lot of hawks out there that will talk a big game, but might not play it.